The field of the invention is acoustic enclosures, and more particularly, acoustic enclosures used to attenuate noise from marine engine generator sets.
Engine generator sets are often used as a source of electrical power on boats. Typically, a marine engine drives an alternator with a rating that ranges from 10 to 50 Kilowatts (KW). Enclosures are often desired for such engine generator sets to attenuate the engine noise. One common practice, as taught in U.S. Pat. No. 4,516,657 to Allard, is to reduce all external openings in the enclosure to a minimum to reduce noise leakage. However, the enclosure must also allow sufficient air flow to cool the interior components. If apertures in the enclosure are minimized, the cooling air flow can be overly restricted, necessitating that the generator be derated, e.g. operated at less than full capacity, to avoid overheating. In this regard, it is the cooling requirements for the generator, not the engine, which are the more stringent. This is especially poignant in marine applications where the engine is usually cooled by circulating sea water through a heat exchanger with the engine coolant. The engine is therefore cooled externally and the need for air flow to cool the engine is drastically reduced as compared to air cooled or radiator cooled engines. For such marine applications, the accepted practice is to enclose the engine generator set in an acoustical box with minimum ventilation, since the engine is externally cooled and maximum noise attenuation is desired. It is then necessary, however, to derate the generator accordingly due to the elevated ambient temperature inside the acoustical box. Even a small restriction in cooling for the alternator will result in some derating, as the generator is usually rated for free air operation. Therefore, the approach used in prior applications has been to oversize the generator to allow sufficient capacity for the electrical load to be served after the derating caused by the acoustic enclosure has been accounted for.